A constant speed control apparatus is known which enables an automotive vehicle to run constantly at a speed predetermined by a driver while the accelerator, normally a foot-operated pedal, remains undepressed by the driver. The known constant speed control apparatus is arranged such that an actuator is activated upon receiving a constant speed control command and allows a cruise cable to actuate a throttle valve for specific opening and closing thereof.
Such a constant speed control apparatus is disclosed in Japanese Patent Publication No. 61-291225 (1986), in which if a brake switch or relay is inoperable and thus fails to cancel (i.e. shut off) the constant speed control system when the brake is actuated, a trouble detecting arrangement detects a fault in the system and then, according to the detected information, a control arrangement actuates the throttle valve for returning it to the neutral position to thus cancel the constant speed running and ensure safe driving.
The prior art constant speed control apparatus incorporates a command switch acting as a control switch and a cancel switch acting as a reset switch and connected to a main isolator switch for the main power supply. The main power supply switch may be either activated in relation to an ignition switch or turned on and off independently of the ignition switch. Accordingly, the main power supply switch as connected and disconnected independently of the ignition switch is commonly kept closed for the purpose of constant power supply to the control arrangement. As a result, when the running speed of the vehicle exceeds a specified speed with the control switch (e.g. a set switch) being turned on, the vehicle continues to run at an incremental (i.e. varying) speed or at a constant speed but under no control, thus creating a disadvantage in the control.
A primary object of the present invention is to overcome the aforesaid problem by enabling a vehicle constant speed control apparatus to detect, at an early stage, a malfunction wherein the control switch is closed at the time the main power supply switch is switched on and to stop (i.e. shut off or deactivate) the constant speed control of the vehicle so that the vehicle can be prevented from running under no control, thus improving its safety.